Nickel alloy

ABSTRACT

A nickel alloy of improved premeability having about 75 to 80 percent nickel, about 1.75 to 3.5 percent chromium, about 3 to 7 percent copper, a critical maximum sulfur limit of less than 0.003 percent and the balance iron. The nickel and chromium contents in the alloy are present in balanced combinations which have been found to provide unexpectedly superior magnetic properties.

United States Patent Zukas et al.

NICKEL ALLOY Robert C. Zukas, Natrona Heights; Robert C. McMath, Vandegrift, both of Pa.

Allegheny Ludlum Steel Corporation, Pittsburgh, Pa.

Mar. 2, 1970 Inventors:

Assignee:

Filed:

Appl. No.:

US. Cl ..75/171, 148/3155, 148/120,

148/121 Int. Cl ..C22c 19/00 Field of Search ..75/171, 170; 148/32, 32.5,

[ 1 Mar. 14, 1972 [56] References Cited UNITED STATES PATENTS 3,553,035 l/l971 Colling et al ..l48/l2l Primary Examiner-Richard 0. Dean Attomey--Richard A. Speer, Vincent G. Gioia and Howard R. Berkenstock [57] ABSTRACT 4 Claims, 1 Drawing Figure -5.0 '4 b L l 2.60 O Q b k [.80 /.75 I I I 96 NICKEL NICKEL ALLOY A nickel alloy which has received considerable use in electrical applications because of its superior magnetic properties is one commonly known in the industry as mumetal." This alloy is a combination of nickel, chromium, copper and iron. Typical commercial alloys of mumetal additionally contain aluminum, titanium, phosphorus, and sulfur in spite of the fact that it has been known that excessive quantities of these materials have undesirable effects on magnetic properties.

It has now been discovered that alloys that contain nickel, chromium, copper, and iron can be formulated with substantially improved electrical properties by carefully balancing the nickel and chromium contents with respect to each other and by maintaining sulfur below a critical limit of 0.003 percent. More specifically, alloys in accordance with the invention contain about 75 to 80 percent nickel, about 1.75 to 3.5 percent chromium, about 3 to 7 percent copper, less than 0.003 percent sulfur, preferably not greater than 0.002 percent sulfur, and the balance iron. In addition, however, the nickel and chromium contents are carefully restricted with respect to each other. The importance of critically relating the nickel and chromium contents can be seen by examination of the tables below which describe alloys containing these elements within the aforementioned numerical ranges, but either (1) not balanced with respect to each other in accordance with the invention, or (2) sulfur exceeds the critical requirement of less than 0.003 percent.

A series of heats having compositions defined in Table I were prepared and produced in strip form of 0.014 inch thickness. Desirable magnetic properties are developed by high temperature annealing followed by controlled cooling at a rate of 100 to l,000 F. per hour. The composition and DC permeability of these compositions are shown in Table 1.

TABLE 1 Heat 100 gauss No. Ni '17 Cr Cu 36 S 90 Fe DC Permeability 81618 76.2 2.46 5.08 0.005 Bali 87,700 81383 76.2 2.75 5.55 0.006 Bal. 86,200 8824 76.7 2.61 5.00 0.003 Bal. 87,000 81990 77.4 2.28 4.80 0.002 Bal. 50,000

0.05 inch thick sample The permeability of the compositions shown above in Table I can be compared with others having elements also falling within the prescribed numerical range but which, in addition, have the nickel and chromium contents carefully balanced with respect to each other and sulfur under 0.003 percent. These heats, of the chemistries shown in Table II, were lt is evident from a comparison of the properties reported in Tables 1 and 11 that by maintaining a balance between the nickel and chromium contents and, in addition, observing a low, critical limit on the sulfur content, the permeability of the alloy may be improved from less than 90,000 to well over 130,000. All of the examples have a 100 gauss DC permeability of over 120,000. This represents a substantial improvement in the beneficial electrical properties of the alloy produced. The first three heats in Table I have balanced nickel and chromium contents but the sulfur is 0.003 percent or greater. In this connection it is noteworthy that 0.003 percent sulfur in heat 8824 is too high and the permeability is substantially less then alloys with less than 0.003 percent sulfur, as shown in Table 11. Heat 81990 in Table 1 has desirably low sulfur, i.e., 0.002 percent, but the nickel and chromium contents are not properly balanced and, accordingly, the permeability is low.

With each nickel level between about 75 and percent, there exists a chromium level which is capable of developing unusually high magnetic properties. When the nickel level is outside the specified range, the magnetic properties cannot be developed within the desired cooling rates of per hour to 1,000 F. per hour. 1n the curve of the accompanying drawing, the nickel and chromium contents are plotted against each other so that combinations of nickel and chromium can be selected which will result in alloys having superior magnetic properties. A number of alloys having desirable properties are listed in Table 111. The nickel and chromium contents are related to each other in the manner illustrated in the curve.

Referring to the chart in the drawing, lines A and B define the zone within which the properly balanced nickel and chromium compositions appear. Line C represents the optimum balancing of these elements, however the area between lines A" and B will provide related nickel and chromium content with superior properties.

We have found that the copper content within the range of 3 to 7 percent does not affect the properties as much as nickel and chromium. However, in order to optimize the properties still further, it is desirable to relate the copper content to the nickel and chromium as shown on the curve in the drawing. Thus, for example, with 2.8 percent chromium (line d e), the nickel content can extend from about 76.2 (line d f to about 77.6 percent (point e). For optimum properties, at 2.8 percent chromium and 76.2 percent nickel, the copper content should be between about 4.8 percent (line d e) to 6.2 percent (point f). At 2.8 percent chromium and 77.6 percent nickel, the copper content should be between 4.8 percent (line d e) and 3.3 percent (point 3). Preferred nickel and copper contents for 2.8 percent chromium (point h) would be about 76.9 percent nickel (line m n) and about 4.0 percent copper (point m) to about 5.5 percent copper (point n).

Alloys of the invention may additionally contain certain other elements which do not unduly interfere with the desirably high magnetic properties. Among these elements are manganese, silicon and carbon. As much as 1.5 percent manganese has been found to be includable without detrimentally affecting the magnetic properties. Similarly, silicon may be included up to 1.0 percent and carbon up to 0.05 percent. In general, however, impurities should be maintained as low as possible. This may be advantageously done by vacuum melting the alloy which greatly minimizes the risk of contamination. Other melting techniques such as consumable electrode remelting or electroslag remelting may also be employed with advantage due to the ability to control impurity levels by these melting practices.

It is apparent from the above that various changes and panying drawing. modifications may be made without departing from the inven- 2. An alloy according to claim 1 wherein the quantities of tion. Accordingly, the scope thereof should be limited only by nickel, hr mi m and pp are selected, wi hin h respecthe appended claims wherein what is claimed is: tive ranges of each, so as to come within lines A" and B of We claim: 5 the graph in the accompanying drawing. 1. An alloy consisting essentially of about 75 to 80 percent 3. An alloy according to claim 1 wherein the sulfur content nickel, about 1.75 to 3.5 percent chromium, about 3 to 7 per- 15 not g than 9 p cent copper, less than 0.003 percent sulfur, and the balance alloy aoccordmg to Claim 1 hlCh. after annealmg at essentially iron, and wherein the nickel and chromium con- 2,000 to 2,200 and cooling at a "fi of 100 to 1,000 tents are selected, within the respective ranges of each, so as 10 Per hour has a 100 gauss DC Permeab'my ofover 120900 to come within lines A and 8" of the graph in the accom- 

2. An alloy according to claim 1 wherein the quantities of nickel, chromium and copper are selected, within the respective ranges of each, so as to come within lines ''''A'''' and ''''B'''' of the graph in the accompanying drawing.
 3. An alloy according to claim 1 wherein the sulfur content is not greater than 0.002 percent.
 4. An alloy according to claim 1 which, after annealing at 2, 000* to 2,200* F. and cooling at a rate of 100* to 1,000* F. per hour, has a 100 gauss DC permeability of over 120,000. 